1. Field of the Invention
The present invention relates to printed circuit boards (PCBs), and particularly to a PCB which can reduce crosstalk between signal traces in the PCB, and can save space of the PCB.
2. Description of Related Art
The advancement of electronic industry demands more and more electronic components to be integrated on a single PCB. Additionally, smaller PCBs are demanded for smaller electronic products. As a result, a PCB with a limited area requires disposing components thereon more densely. This narrows the spacing between signal traces.
Conventionally, a PCB adopts a right-angle routing scenario, a 45 degree routing scenario, a differential routing scenario, or a zigzag routing scenario. In high-speed design applications, one usually employs the differential routing scenario.
Referring to FIG. 1, a partial cross-sectional view of a conventional PCB is illustrated. As shown, the PCB includes a first signal layer 100, a second signal layer 200, a first dielectric layer 300, a second dielectric layer 400, a third dielectric layer 500, a first ground layer 600, and a second ground layer 700, wherein a plurality of differential pairs, such as a first differential pair 120 and a second differential pair 140, are respectively disposed within the first signal layer 100 and the second signal layer 200. The first signal layer 100 is formed between the first dielectric layer 300 and the second dielectric layer 400. The second signal layer 200 is formed between the second dielectric layer 400 and the third dielectric layer 500. The first dielectric layer 300 is formed between the first signal layer 100 and the first ground layer 600. The third dielectric layer 500 is formed between the second signal layer 200 and the second ground layer 700. The first differential pair 120 includes a positive differential trace TX+ and a negative differential trace TX−. The second differential pair 140 includes a positive differential trace RX+ and a negative differential trace RX−. The first ground layer 600 is configured to supply a circuit path for the first differential pair 120. The second ground layer 700 is configured to supply a circuit path for the second differential pair 140.
However, the conventional PCB, illustrated in FIG. 1, is disadvantageous in that each of the differential pairs is disposed in a single signal layer, which allows crosstalk between two differential pairs respectively disposed within two adjacent signal layers. Furthermore, each conventional ground area is formed as an independent layer, which occupies lots of space of the PCB.
What is desired, therefore, is to provide a PCB which overcomes the above problems.